I'm moving a mail server from one CentOS 6 to another. I use sendmail with sasl pam authentication. When I try to send mail it fails because the user is not authenticated and the mail client does not require password. All the configurations files are the same on both new and old servers. I tested this with telnet (new server):

I had this problem and installing cyrus-sasl-plain fixed it for me. Thanks for the tip! Auth works for me now. Unless you specifically need those other auth mechanisms, try removing EXTERNAL DIGEST-MD5 CRAM-MD5 and leave only LOGIN PLAIN. If your connection is TLS then PLAIN should be sufficient.
– IanBFeb 11 '16 at 5:38

Well it seams that the only problem was that I didn't have package cyrus-sasl-plain installed on the new server. After restarting all services (saslauthd and sendmail) and also the mail client sending and authenticating worked fine.